New stealthy botnet Trojan holds Facebook users hostage

A new strain of cybercrime Trojan is targeting Facebook users by taking over their machines and shaking them down for cash.

Carberp, like its predecessors ZeuS and SpyEye, infects machines by tricking punters into opening PDFs and Excel documents loaded with malicious code, or attacks computers in drive-by downloads. The hidden malware is designed to steal account information, and harvest credentials for email and social-networking sites.

A new configuration of the Carberp Trojan targets Facebook users to ultimately steal e-cash vouchers. Previous malware attacks on Facebook have been designed purely to slurp login info, so this latest skirmish, spotted by transaction security firm Trusteer, can be considered something of an escalation.

The Carberp variant replaces any Facebook page the user navigates to with a fake page notifying the victim that their Facebook account is temporarily locked. Effectively holding Facebook users hostage, the page asks the mark for their first name, last name, email, date of birth, password and a Ukash 20 euro ($25) voucher number to verify their identity and unlock the account.

Trusteer warns the cash voucher attack is in some ways worse than credit card fraud, because with e-cash it is the account-holder, not the financial institution, who assumes the liability for fraudulent transactions.

Trusteer said it does not have any concrete data on how many people might have been hit by this particular attack. But it warns social networking users, particular those with e-cash accounts, to be wary of this particular scam and potential follow-up frauds along the same lines, which might easily trap the unwary.

Amit Klein, CTO at Trusteer, commented: "The fraud technique is quite effective. Keep in mind that the user gets an authentic-looking message in the context of a genuine, deliberate log-in to Facebook. We do know that this is exactly where users are most susceptible to divulging personal information and following additional instructions, as their trust in the content is maximal."

The use of anti-debugging and rootkit techniques make Carberp Trojan difficult to detect, warns security consultancy Context Information Security. Context said: "Carberp is also part of a botnet that can take full control over infected hosts, while its complicated infection mechanisms and extensive functionality make it a prime candidate for more targeted attacks."

Context adds that Carberp, which creates a backdoor on infected machines, can be controlled from a central administrator control panel, allowing botnet herders to more easily mine stolen data.

Trusteer said it had reported the attack to Facebook, and shared malware samples prior to giving live with its blog, a day after Facebook boasted it had been free of the Koobface worm for more than nine months.

"I don't think that this incident contradicts their "virus free" statement, since Carberp only infects the victim PCs without any modification of the victim's profile in Facebook or any other alteration of the Facebook site," Trusteer's CTO told El Reg. "And to the best of our knowledge, Carberp does not propagate through Facebook."

Trusteer published a blog post on Wednesday featuring screenshots of more details of the Carberp e-cash scam in action in a blog post ®